India started its own nuclear program in 1944 when Homi J. Bhabha founded the Tata Institute of Fundamental Research.[4] Physicist Raja Ramanna played an essential role in nuclear weapons technology research; he expanded and supervised scientific research on nuclear weapons and was the first directing officer of the small team of scientists that supervised and carried out the test.[4]

We must develop this atomic energy quite apart from war — indeed I think we must develop it for the purpose of using it for peaceful purposes. ... Of course, if we are compelled as a nation to use it for other purposes, possibly no pious sentiments of any of us will stop the nation from using it that way.

In 1954, Bhabha steered the nuclear program in the direction of weapons design and production. Two important infrastructure projects were commissioned. The first established Trombay Atomic Energy Establishment at Mumbai (Bombay). The other created a governmental secretariat, Department of Atomic Energy (DAE), of which Bhabha was the first secretary. From 1954 to 1959, the nuclear program grew swiftly. By 1958, the DAE had one-third of the defense budget for research purposes.[4] In 1954, India reached a verbal understanding with the United States and Canada under the Atoms for Peace program; the United States and Canada ultimately agreed to provide and establish the CIRUS research reactor also at Trombay. The acquisition of CIRUS was a watershed event in nuclear proliferation with the understanding between India and the United States that the reactor would be used for peaceful purposes only.[4] CIRUS was an ideal facility to develop a plutonium device, and therefore Nehru refused to accept nuclear fuel from Canada and started the program to develop an indigenous nuclear fuel cycle.[4]

In July 1958, Nehru authorized "Project Phoenix" to build a reprocessing plant with a capacity of 20 tons of fuel a year – a size to match the production capacity of CIRUS[clarification needed].[4] The plant used the PUREX process and was designed by the American firm Vitro International.[4] Construction of the plutonium plant began at Trombay on 27 March 1961, and it was commissioned in mid-1964.[4]

The nuclear program continued to mature, and by 1960, Nehru made the critical decision to move the program into production.[4] At about the same time, Nehru held discussions with the American firm Westinghouse Electric to construct India's first nuclear power plant in Tarapur, Maharashtra.[4]Kenneth Nichols, a US Army engineer, recalls from a meeting[6] with Nehru, "it was that time when Nehru turned to Bhabha and asked Bhabha for the timeline of the development of a nuclear weapon". Bhabha estimated he would need about a year to accomplish the task.[4]

By 1962, the nuclear program was still developing, but at a slow rate. Nehru was distracted by the Sino-Indian War, during which India lost territory to China.[4] Nehru turned to the Soviet Union for help, but the Soviet Union was preoccupied with the Cuban Missile Crisis.[4] The Soviet Politburo turned down Nehru's request for arms and continued backing the Chinese.[4] India concluded that the Soviet Union was an unreliable ally, and this conclusion strengthened India's determination to create a nuclear deterrent.[4] Design work began in 1965 under Bhabha and proceeded under Raja Ramanna who took over the program after the former's death.[4]

Bhabha was now aggressively lobbying for nuclear weapons and made several speeches on Indian radio.[7] In 1964, Bhabha told the Indian public via Indian radio that "such nuclear weapons are remarkably cheap" and supported his arguments by referring to the economical cost of American nuclear testing programme (Plowshare).[7] Bhabha stated to the politicians that a 10 kt device would cost around $350,000, and $600,000 for a 2 Mt.[7] From this, he estimated that "a stockpile" of around 50 atomic bombs would cost under $21 million and a stockpile of 50 two-megaton hydrogen bombs would cost around $31.5 million."[7] Bhabha did not realize, however, that the U.S. Plowshare cost-figures were produced by a vast industrial complex costing tens of billions of dollars, which had already manufactured nuclear weapons numbering in the tens of thousands.[7] The delivery systems for nuclear weapons typically cost several times as much as the weapons themselves.[7]

The nuclear program was partially slowed down when Lal Bahadur Shastri became the prime minister.[8] In 1965, Shastri faced another war with Pakistan. Shastri appointed physicist Vikram Sarabhai as the head of the nuclear programme but because of his Gandhian beliefs Sarabhai directed the programme toward peaceful purposes rather than military development.[8]

In 1967, Indira Gandhi became the prime minister and work on the nuclear program resumed with renewed vigor.[4]Homi Sethna, a chemical engineer, played a significant role in the development of weapon-grade plutonium while Ramanna designed and manufactured the whole nuclear device.[8] The first nuclear bomb project did not employ more than 75 scientists because of its sensitivity.[8] The nuclear weapons programme was now directed towards the production of plutonium rather than uranium.[9]

In 1968–69, P. K. Iyengar visited the Soviet Union with three colleagues and toured the nuclear research facilities at Dubna, Russia.[9] During his visit, Iyengar was impressed by the plutonium-fueled pulsed fast reactor.[9] Upon his return to India, Iyengar set about developing plutonium reactors approved by the Indian political leadership in January 1969.[9] The secret plutonium plant was known as Purnima,[10] and construction began in March 1969. The plant's leadership included Iyengar, Ramanna, Homi Sethna, and Sarabhai. Sarabhai's presence indicates that, with or without formal approval, the work on nuclear weapons at Trombay had been commenced.[9]

India continued to harbour ambivalent feelings about nuclear weapons, and accorded low priority to their production until the Indo-Pakistani War of 1971. In December 1971, Richard Nixon sent a carrier battle group led by the USS Enterprise (CVN-65) into the Bay of Bengal in an attempt to intimidate India. The Soviet Union responded by sending a submarine armed with nuclear missiles from Vladivostok to trail the US task force. The Soviet response demonstrated the deterrent value and significance of nuclear weapons and ballistic missile submarines to Indira Gandhi.[11] India gained the military and political initiative over Pakistan after acceding to the treaty that divided Pakistan into two different political entities.[9]

On 7 September 1972, near the peak of her post-war popularity, Indira Gandhi authorized the Bhabha Atomic Research Centre (BARC) to manufacture a nuclear device and prepare it for a test.[5] Although the Indian Army was not fully involved in the nuclear testing, the army's highest command was kept fully informed of the test preparations.[9] The preparations were carried out under the watchful eyes of the Indian political leadership, with civilian scientists assisting the Indian Army.[2]

The nuclear yield of this test still remains controversial, with unclear data provided by Indian sources, although Indian politicians have given the country's press a range from 2 kt to 20 kt.[2] The official yield was initially set at 12 kt; post-Operation Shakti claims have raised it to 13 kt.[2] Independent seismic data from outside and analysis of the crater features indicate a lower figure.[2] Analysts usually estimate the yield at 4 to 6 kt, using conventional seismic magnitude-to-yield conversion formulas. In recent years, both Homi Sethna and P. K. Iyengar have conceded the official yield to be an exaggeration.[2]

Iyengar has variously stated that the yield was actually 8–10 kt, that the device was designed to yield 10 kt, and that the yield was 8 kt "exactly as predicted". Although seismic scaling laws lead to an estimated yield range between 3.2 kt and 21 kt,[16] an analysis of hard rock cratering effects suggests a narrow range of around 8 kt for the yield,[2] which is within the uncertainties of the seismic yield estimate.[16]

The Pokhran test was a bomb, I can tell you now.... An explosion is an explosion, a gun is a gun, whether you shoot at someone or shoot at the ground.... I just want to make clear that the test was not all that peaceful.

While India continued to state that the test was for peaceful purposes, it encountered opposition from many quarters. The Nuclear Suppliers Group (NSG) was formed in reaction to the Indian tests to check international nuclear proliferation.[18] The NSG decided in 1992 to require full-scope IAEA safeguards for any new nuclear export deals,[19] which effectively ruled out nuclear exports to India, but in 2008 it waived this restriction on nuclear trade with India as part of the Indo-US civilian nuclear agreement.[20]

The plutonium used in the test was created in the CIRUS reactor supplied by Canada and using heavy water supplied by the United States. Both countries reacted negatively, especially in light of then ongoing negotiations on the Nuclear Non-Proliferation Treaty and the economic aid both countries had provided to India.[5][24] Canada concluded that the test violated a 1971 understanding between the two states, and froze nuclear energy assistance for the two heavy water reactors then under construction.[5] The United States concluded that the test did not violate any agreement and proceeded with a June 1974 shipment of enriched uranium for the Tarapur reactor.[5]

Despite many proposals, India did not carry out further nuclear tests until 1998. After the 1998 general elections, Operation Shakti (also known as Pokhran-II) was carried out at the Pokhran test site, using devices designed and built over the preceding two decades.[5][26]